Problem: Simplify the following expression: $q = \dfrac{z}{7} + \dfrac{z}{9}$
In order to add expressions, they must have a common denominator. The smallest common denominator is the least common multiple of $7$ and $9$ $\lcm(7, 9) = 63$ $ q = \dfrac{9}{9} \cdot \dfrac{z}{7} + \dfrac{7}{7} \cdot \dfrac{z}{9} $ $q = \dfrac{9z}{63} + \dfrac{7z}{63}$ $q = \dfrac{9z +7z}{63}$ $q = \dfrac{16z}{63}$